1. Field of the Invention
The present invention relates to an inverter power generator that generates AC power with a synchronous motor driven by a prime mover such as an engine, converts the AC power into DC power, and inverts the DC power with an inverter into AC power of a required frequency.
2. Description of Related Art
The inverter power generator is widely used to generate electric power with the use of a prime mover such as an engine. The inverter power generator connects an output shaft of the engine to a rotary shaft of a synchronous motor, drives the synchronous motor with the engine to generate AC power, converts the AC power with a converter into DC power, and inverts the DC power with an inverter into AC output power of required voltage and frequency. The AC output power is supplied to a load such as a motor, a lamp, or the like that is connected to the inverter.
An example of the inverter power generator is disclosed in Japanese Unexamined Patent Application Publication No. 2010-110062 (Patent Document 1). This related art calculates power generated by an engine before and after a change occurs in a load, finds a difference in the generated power between before and after the load change, and if the difference is larger than a threshold, increases the rotation speed of the engine. This technique changes the rotational speed of the engine without loosing a good operation feeling.
To improve energy efficiency, the inverter power generator is required to reduce the rotational speed of the engine as low as possible. Driving the engine at low speed, however, causes a problem when the load suddenly changes to increase power demand of the converter. To meet the increased power demand, the engine must increase its rotational speed. The engine, however, is unable to rapidly increase its rotational speed and to stall.